Redundant multicast trees without duplication and with fast recovery

ABSTRACT

In an example method for redundant multicast trees with fast recovery, a protocol independent multicast (PIM) backup designated router (BDR) can receive a request from a host to join a multicast group associated with a source; send to a next hop a PIM join message identifying an address of the PIM BDR and identifying the PIM join message as a backup PIM join; receive, from a PIM router along a path to/from the source, a unicast message sent to the address which identifies a second address associated with the PIM router; store the second address and a route associated with the unicast message; in response to a designated router migration trigger, set to blocking a backup multicast tree state associated with the source and multicast group; and send, to the PIM router, a unicast message including instructions to set to blocking a backup multicast tree state at the PIM router.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 16/289,455, filed Feb. 28, 2019, the content ofwhich is hereby expressly incorporated by reference in its entirety.

TECHNICAL FIELD

The present technology pertains to multicast routing, and morespecifically to implementing redundant multicast trees with fastrecovery for multicast routing.

BACKGROUND

Traditional Internet Protocol (IP) communication allows a host to sendpackets to a single destination through unicast transmission orbroadcast packets to an entire network segment through broadcasttransmission. In addition, IP multicast technologies allow a host tosend packets to a subset of hosts as a group or multicast transmission.Unicast transmissions use unicast addresses to send packets to singledestinations associated with the unicast addresses. Broadcasttransmissions use broadcast addresses to send packets to entire networksegments or subnetworks. Multicast transmissions use multicast addressesto send packets to subsets of hosts configured as members of respectivemulticast groups. The members of a multicast group can reside on a samenetwork or different networks.

IP multicast can conserve bandwidth by reducing traffic throughsimultaneous delivery of a stream of information to numerous recipients.Typically, multicast packets are replicated at a point where pathsdiverge using multicast protocols such as Protocol Independent Multicast(PIM), thereby delivering source traffic to multiple receivers withoutburdening the source or receivers and while utilizing a limited amountof network resources. Not surprisingly, IP multicast has gainedconsiderable popularity as demand for multicast traffic continues togrow. For example, IP multicast is increasingly implemented in a widevariety of applications such as, for example, video conferencing,enterprise communications, and distribution of software and information.

At the same time, IP multicast can be significantly complex to implementand despite its numerous benefits, current IP multicast solutions facedifficult challenges that can negatively impact the cost, performanceand stability of multicast deployments. For example, in multicastdeployments, multicast-capable routing devices use a multicast routingprotocol to build a distribution tree for each multicast group. Thedistribution tree represents the multicast path(s) or state and allowssources to send packets to receivers. The distribution tree is updatedperiodically as nodes join or leave the multicast group or the topologychanges. Moreover, a single point of failure can affect the distributiontree, requiring the network to reconstruct or repair the distributiontree. However, the process of updating or reconstructing thedistribution tree can take time, which can cause disruption in multicastservices and communications until the process completes and the networkconverges. The process also involves a significant amount of networkcommunications, often including duplicate traffic. This traffic cansignificantly burden the network, thereby increasing cost and reducingnetwork and service performance.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the disclosure can be obtained, a moreparticular description of the principles briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only exemplary embodiments of the disclosure and are nottherefore to be considered to be limiting of its scope, the principlesherein are described and explained with additional specificity anddetail through the use of the accompanying drawings in which.

FIG. 1 illustrates an example model for PIM services, in accordance withsome examples;

FIG. 2A illustrates an example PIM services deployment with active andbackup designated routers in an example topology with disjoint paths, inaccordance with some examples;

FIG. 2B illustrates an example PIM services deployment with active andbackup designated routers in an example topology with a merged path, inaccordance with some examples:

FIG. 2C illustrates an example PIM services deployment with active andbackup designated routers in an example topology with a merged path anda different network that overlaps with a current backup multicastdistribution tree, in accordance with some examples;

FIG. 3A illustrates an example flow for processing active PIM joinsassociated with a multicast group and source, in accordance with someexamples;

FIG. 3B illustrates an example flow for processing backup PIM joinsassociated with a multicast group and source, in accordance with someexamples;

FIG. 3C illustrates an example flow for performing a designated routermigration, in accordance with some examples,

FIG. 4A illustrates an example flow for processing backup PIM joinsassociated with a multicast group and source in an example topology witha merged path, in accordance with some examples;

FIG. 413 illustrates an example flow for performing a designated routermigration in an example topology with a merged path, in accordance withsome examples;

FIG. 5 illustrates an example flow for processing active PIM joinsassociated with a multicast group and source in an example topology witha merged path and a network that overlaps with a current backupmulticast distribution tree, in accordance with some examples;

FIG. 6 illustrates an example method for establishing an active PIM DR,an active multicast tree state, and an active multicast path, inaccordance with some examples;

FIG. 7 illustrates an example method for establishing a backup PIM DRand backup multicast path, and performing a DR migration, in accordancewith some examples;

FIG. 8 illustrates a flowchart of an example method for processing PIMjoin messages and performing a DR migration at a merge point in a PIMdeployment, in accordance with some examples;

FIG. 9 illustrates an example network device in accordance with someexamples; and

FIG. 10 illustrates an example computing device architecture inaccordance with some examples.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Various embodiments of the disclosure are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the disclosure.Thus, the following description and drawings are illustrative and arenot to be construed as limiting. Numerous specific details are describedto provide a thorough understanding of the disclosure. However, incertain instances, well-known or conventional details are not describedin order to avoid obscuring the description. References to one or anembodiment in the present disclosure can be references to the sameembodiment or any embodiment; and, such references mean at least one ofthe embodiments.

Reference to “one embodiment” or “an embodiment” means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the disclosure. Theappearances of the phrase “in one embodiment” in various places in thespecification are not necessarily all referring to the same embodiment,nor are separate or alternative embodiments mutually exclusive of otherembodiments. Moreover, various features are described which may beexhibited by some embodiments and not by others.

The terms used in this specification generally have their ordinarymeanings in the art, within the context of the disclosure, and in thespecific context where each term is used. Alternative language andsynonyms may be used for any one or more of the terms discussed herein,and no special significance should be placed upon whether or not a termis elaborated or discussed herein. In some cases, synonyms for certainterms are provided. A recital of one or more synonyms does not excludethe use of other synonyms. The use of examples anywhere in thisspecification including examples of any terms discussed herein isillustrative only, and is not intended to further limit the scope andmeaning of the disclosure or of any example term. Likewise, thedisclosure is not limited to various embodiments given in thisspecification.

Without intent to limit the scope of the disclosure, examples ofinstruments, apparatus, methods and their related results according tothe embodiments of the present disclosure are given below. Note thattitles or subtitles may be used in the examples for convenience of areader, which in no way should limit the scope of the disclosure. Unlessotherwise defined, technical and scientific terms used herein have themeaning as commonly understood by one of ordinary skill in the art towhich this disclosure pertains. In the case of conflict, the presentdocument, including definitions will control.

Additional features and advantages of the disclosure will be set forthin the description which follows, and in part will be obvious from thedescription, or can be learned by practice of the herein disclosedprinciples. The features and advantages of the disclosure can berealized and obtained by means of the instruments and combinationsparticularly pointed out in the appended claims. These and otherfeatures of the disclosure will become more fully apparent from thefollowing description and appended claims, or can be learned by thepractice of the principles set forth herein.

Overview

Disclosed are systems, methods, and computer-readable media forimplementing redundant multicast trees with fast recovery and without(or with limited) duplication. In some examples, a method is providedfor implementing redundant multicast trees with fast recovery andwithout (or with limited) duplication. In some examples, the method caninclude receiving, by a protocol independent multicast (PIM) backupdesignated router (BDR), a request from a host device to join amulticast group associated with a source of multicast traffic. The hostdevice can be a receiver requesting membership in the multicast group(e.g., multicast group G) associated with the source (e.g., source S) ofmulticast traffic. The request from the host device can be a messageexpressing interest in receiving traffic destined for the multicastgroup (e.g., G) from the source (e.g., S). The host device can send therequest to the PIM BDR using any communications protocol suitable forestablishing multicast group memberships, such as Internet GroupManagement Protocol (IGMP) for example.

The PIM BDR can be configured as a backup designated router (DR) forredundancy. A DR is a PIM-capable router that can act on behalf ofhost(s) connected to the DR (e.g., via a shared local area network orLAN) with respect to PIM operations and signaling. A DR can be electedthrough an election process for an interface (e.g., a LAN or otherwise)to serve as a DR for members or receivers on that interface or network.As previously mentioned, the PIM BDR can be configured as a backup DR torun on standby mode (and/or non-forwarding mode) while another DR isactive, and switch to active mode (and/or forwarding mode) if there is afailure or problem (e.g., an access link failure, a core link failure, aPIM router failure, etc.) that can be fixed or addressed by migratingthe active DR role to the PIM BDR.

The method can further include sending, by the PIM BDR in response tothe request, a PIM join message to a next hop (e.g., the next hopPIM-capable router) between the PIM BDR and the source of the multicasttraffic. For example, the PIM BDR can send a PIM join message towardsthe source of multicast traffic and/or a merge point in the path (e.g.,a first hop router (FHR) connected to the source, a rendezvous point(RP) router configured as a root of a multicast tree for the multicastgroup, a PIM router located at a merge point between paths and/or backupand active multicast trees for the multicast group, etc.).

The PIM join message can include attributes (e.g., join attributes)identifying an address of the PIM BDR (e.g., the loopback address of thePIM BDR) and indicating that the PIM join message is a backup PIM joinfrom a backup DR. As further explained below, the address of the PIM BDRcan be included in the PIM join message to inform a merge point router(e.g., RP router, FHR router, etc.) along the path of the PIM joinmessage of an address that can be used to communicate with the PIM BDRthrough unicast communications (e.g., direct or point-to-pointcommunications) to avoid duplicate PIM-related traffic when running thePIM BDR, performing a DR migration, reconstructing or updating amulticast tree, etc. For example, a merge point router, such as an RP orFHR router, that receives the PIM join message can extract and/or storethe address in the attributes of the PIM join message and use theaddress for unicast communications with the PIM BDR for a DR migrationevent.

Moreover, the attribute identifying the PIM join message as a backup PIMjoin can be used to inform a receiving merge point router that the PIMjoin is for a backup multicast tree and/or path, and thus should be setto blocking or non-forwarding mode while an active DR and multicast treeare in use. The attribute in the PIM join message can also inform thereceiving merge point router that the originator of the PIM join message(e.g., the PIM BDR) is a backup DR and is thus not active (e.g., is instandby). The receiving merge point router can use the PIM join messageto build a backup multicast tree state for the multicast group andsource, and can use the attributes identifying the PIM join message as abackup PIM join and the PIM BDR as a backup DR to know that the backupmulticast tree state (and/or the outgoing interface (OIF) associatedwith the backup PIM join) should be set to blocking or non-forwardingstate to avoid conflicts or problems with an active multicast tree statefor the multicast group and/or any PIM router that does not understandthe attribute identifying the PIM join as a backup join or does not knowhow to handle such PIM join messages.

Each PIM router that receives the PIM join message along the way to amerge point router can process the PIM join message by checking if italready has active state for the multicast group (e.g., (S, G)) and,when no active state is found, instantiating multicast state or amulticast entry for the multicast group (e.g., (S, G)), storing theaddress of the PIM BDR in the attributes of the PIM join message, andsending the PIM join message to the next hop. In some cases, whensending the PIM join message to the next hop, a PIM router can alsoinclude its own address as an attribute of the PIM join message toinform other PIM routers along the path of its own address and/orprovide insight on the route taken by the PIM join message. Each hop canprocess the PIM join message similarly and send it along to the nexthop.

As further explained below, when the PIM join message reaches a mergepoint router such as an RP or FHR router, the merge point router candetermine that an active join state is already present, set the OIF ofthe backup PIM join to blocking or non-forwarding state, and use theaddress of the PIM BDR included in the PIM join message to send to thePIM BDR a unicast message. The unicast message to the PIM BDR caninclude, as part of the unicast message (e.g., in the header), anaddress of the merge point router, which the PIM BDR can use to sendunicast messages (e.g., PIM-related unicast communications) to the mergepoint router, thereby using point-to-point signaling instead ofhop-by-hop signaling and thus reducing or eliminating duplicate traffic.

For example, after the PIM join message has been received and processedby a merge point router, the method can include receiving, by the PIMBDR, from a PIM router located along a path between the PIM BDR and thesource of the multicast traffic (e.g., a merge point router such as anRP or FHR router), a first unicast message sent to the address of thePIM BDR identified in the PIM join message. The first unicast messagecan identify or include (e.g., in the header) an address of the PIMrouter, which the PIM BDR can obtain to use to send unicast messages tothe PIM router. In some cases, the method can include storing, by thePIM BDR, the address associated with the PIM router and a routeassociated with the first unicast message. The route can be identifiedbased on information in the first unicast message (e.g., hops or pathtraversed), for example.

In some cases, multiple PIM BDRs can send such PIM join messages. ThePIM join messages from the different PIM BDRs can have different BDRvalues associated with the different PIM BDRs and/or PIM join messages.When a PIM router receives backup PIM joins from different PIM routersfor a multicast group (e.g., (S, G)), the PIM router can obtain thedifferent BDR values from the backup PIM joins. The PIM router can thensend a backup PIM join upstream containing the BDR values (e.g., a listof BDR addresses). After receiving the backup PIM join, the merge pointrouter can use the listed BDR addresses to send a unicast message toeach of the listed BDR addresses.

The method can further include changing, in response to a DR migrationtriggering event, a first instance of a backup multicast tree state atthe PIM BDR from blocking to forwarding. The first instance of thebackup multicast tree state can be the backup multicast tree statestored at the PIM BDR for the multicast group and source. The backupmulticast tree state can thus be backup multicast state associated withthe source of the multicast traffic and the multicast group (e.g., (S,G) state). Moreover, the backup multicast tree state can include abackup multicast distribution tree for the multicast group and source.

The DR migration triggering event can be any condition, activity orevent configured to trigger the migration of the DR role and/or activemulticast tree state from an active PIM DR to a backup or standby PIM DR(e.g., PIM BDR). For example, the DR migration triggering event can bean access interface failure (e.g., an access interface going down), acore link failure, a failure experienced by one or more PIM routers(e.g., one or more PIM routers going down), and/or any other event orcondition that may interfere with or cause errors or disruption withmulticast routing and communications using a currently-active pathand/or PIM DR. The DR migration triggering event can thus triggermigration of DR roles and multicast tree states (e.g., from an active toa backup multicast tree state and vice versa).

The method can also include sending, by the PIM BDR to the PIM router, asecond unicast message including an instruction to change a secondinstance of the backup multicast tree state at the PIM router fromblocking to forwarding. The second instance of the backup multicast treestate can be the backup multicast tree state stored at the PIM routerfor the multicast group and source (e.g., (S, G) state). The secondinstance of the backup multicast tree state can include the backupmulticast distribution tree for the multicast group and source.

In some cases, changing the first instance of the backup multicast treestate from blocking to forwarding and sending the second unicast messagecan include migrating the PIM BDR to a PIM designated router (DR)(e.g.,changing a role of the PIM BDR from backup DR to active PIM DR) andchanging the backup multicast tree state from backup or blocking toactive or forwarding. Moreover, in some cases, upon migrating frombackup DR to active DR, the PIM BDR (now the active PIM DR) can send tothe next hop between the PIM BDR and the source of the multicast trafficone or more PIM join messages at one or more intervals. The PIM joinmessages can be active PIM joins since the PIM BDR is now the active DR.For example, the active PIM DR (e.g., the PIM BDR after migration) cansend periodic PIM join messages upstream. The active joins will beginpropagating to other PIM routers, though in many cases such PIM joinsmay not make any multicast state changes along the way as the completemulticast tree was already constructed in the previous steps.

In some aspects, a system for implementing redundant multicast treeswith fast recovery and without (or with limited) duplication isprovided. An example system can include a PIM BDR including one or moreprocessors and at least one computer-readable storage medium havingstored therein instructions which, when executed by the one or moreprocessors, cause the PIM BDR to receive a request from a host device tojoin a multicast group associated with a source of multicast traffic; inresponse to the request, send a PIM join message to a next hop betweenthe PIM BDR and the source of the multicast traffic, the PIM joinmessage including attributes identifying an address of the PIM BDR andindicating that the PIM join message is a backup PIM join from a backupDR; receive, from a PIM router located along a path between the PIM BDRand the source of the multicast traffic, a first unicast message sent tothe address identified in the PIM join message, the first unicastmessage identifying an address associated with the PIM router; store theaddress associated with the PIM router and a route associated with thefirst unicast message; change, in response to a DR migration triggeringevent, a first instance of a backup multicast tree state at the PIM BDRfrom blocking to forwarding, the backup multicast tree state beingassociated with the source of the multicast traffic and the multicastgroup; and send, to the PIM router, a second unicast message includingan instruction to change a second instance of the backup multicast treestate at the PIM router from blocking to forwarding.

The PIM router can be a merge point router, such as an RP router, an FHRrouter, or a PIM router located at a fork between an active path ormulticast tree and a backup path or multicast tree associated with themulticast group and source. The PIM router can be downstream from thesource of the multicast traffic and upstream from the PIM BDR. Moreover,each PIM-capable router that receives the PIM join message from the PIMBDR along the way to a merge point router (e.g., the PIM router) canprocess the PIM join message by checking if it already has active statefor the multicast group (e.g., (S, G)) and, when no active state isfound, instantiating multicast state or a multicast entry for themulticast group (e.g., (S, G)) storing the address of the PIM BDR in theattributes of the PIM join message, and sending the PIM join message tothe next hop. In some cases, when sending the PIM join message to thenext hop, the sending PIM router can also include its own address as anattribute of the PIM join message to inform other PIM routers along thepath of its own address and/or provide insight on the route taken by thePIM join message. Each hop can process the PIM join message similarlyand send it along to the next hop.

As further explained, when the PIM join message reaches a merge pointrouter (e.g., the PIM router), the merge point router can determine thatan active join state is already present, set the OIF of the backup PIMjoin to blocking or non-forwarding state, and use the address of the PIMBDR in the PIM join message (e.g., in the header) to send to the PIM BDRa unicast message. The unicast message to the PIM BDR can include anaddress of the merge point router, which the PIM BDR can use to sendunicast messages (e.g., PIM-related unicast communications) to the mergepoint router, thereby using point-to-point signaling instead ofhop-by-hop signaling and thus reducing or eliminating duplicate traffic.The address of the merge point router can be included as part of theunicast message (e.g., in the header).

In some cases, changing the first instance of the backup multicast treestate from blocking to forwarding and sending the second unicast messagecan include migrating the PIM BDR to a PIM designated router (DR)(e.g.,changing a role of the PIM BDR from backup DR to active PIM DR) andchanging the backup multicast tree state from backup or blocking toactive or forwarding. Moreover, in some cases, upon migrating frombackup DR to active DR, the PIM BDR (now the active PIM DR) can send tothe next hop between the PIM BDR and the source of the multicast trafficone or more PIM join messages at one or more intervals. The PIM joinmessages can be active PIM joins since the PIM BDR is now the active DR.For example, the active PIM DR (e.g., the PIM BDR after migration) cansend periodic PIM join messages upstream. The active joins can propagateto other PIM routers, though in many cases such PIM joins may not makeany multicast state changes along the way as the complete multicast treewas already constructed in the previous steps.

In some aspects, a non-transitory computer-readable storage medium forimplementing redundant multicast trees with fast recovery and without(or with limited) duplication is provided. An example non-transitorycomputer-readable storage medium can include instructions stored thereinwhich, when executed by one or more processors, cause the one or moreprocessors to receive, at a PIM BDR, a request from a host device tojoin a multicast group associated with a source of multicast traffic; inresponse to the request, send, by the PIM BDR, a PIM join message to anext hop between the PIM BDR and the source of the multicast traffic,the PIM join message including attributes identifying an address of thePIM BDR and indicating that the PIM join message is a backup PIM joinfrom a backup DR; receive, by the PIM BDR, from a PIM router locatedalong a path between the PIM BDR and the source of the multicasttraffic, a first unicast message sent to the address identified in thePIM join message, the first unicast message identifying an addressassociated with the PIM router, store, by the PIM BDR, the addressassociated with the PIM router and a route associated with the firstunicast message; change, in response to a DR migration triggering event,a first instance of a backup multicast tree state at the PIM BDR fromblocking to forwarding, the backup multicast tree state being associatedwith the source of the multicast traffic and the multicast group; andsend, by the PIM BDR to the PIM router, a second unicast messageincluding an instruction to change a second instance of the backupmulticast tree state at the PIM router from blocking to forwarding.

The PIM router can be a merge point router, such as an RP router, an FHRrouter, or a PIM router located at a fork between an active path ormulticast tree and a backup path or multicast tree associated with themulticast group and source. Moreover, the PIM router can be downstreamfrom the source of the multicast traffic and upstream from the PIM BDR.Further, each PIM-capable router that receives the PIM join message fromthe PIM BDR along the way to a merge point router (e.g., the PIM router)can process the PIM join message by checking if it already has activestate for the multicast group (e.g., (S, G)) and, when no active stateis found, instantiating multicast state or a multicast entry for themulticast group (e.g., (S, G)), storing the address of the PIM BDR inthe attributes of the PIM join message, and sending the PIM join messageto the next hop. In some cases, when sending the PIM join message to thenext hop, the sending PIM router can also include its own address as anattribute of the PIM join message to inform other PIM routers along thepath of its own address and/or provide insight on the route taken by thePIM join message. Each hop can process the PIM join message similarlyand send it along to the next hop.

As further explained, when the PIM join message reaches a merge pointrouter (e.g., the PIM router), the merge point router can determine thatan active join state is already present, set the OIF of the backup PIMjoin to blocking or non-forwarding state, and use the address of the PIMBDR included in the PIM join message to send to the PIM BDR a unicastmessage. The unicast message to the PIM BDR can include an address ofthe merge point router, which the PIM BDR can use to send unicastmessages (e.g., PIM-related unicast communications) to the merge pointrouter, thereby using point-to-point signaling instead of hop-by-hopsignaling and thus reducing or eliminating duplicate traffic. Theaddress of the merge point router can be included as part of the unicastmessage (e.g., in the header).

In some cases, changing the first instance of the backup multicast treestate from blocking to forwarding and sending the second unicast messagecan include migrating the PIM BDR to a PIM designated router (DR)(e.g.,changing a role of the PIM BDR from backup DR to active PIM DR) andchanging the backup multicast tree state from backup or blocking toactive or forwarding. Moreover, in some cases, upon migrating frombackup DR to active DR, the PIM BDR (now the active PIM DR) can send tothe next hop between the PIM BDR and the source of the multicast trafficone or more PIM join messages at one or more intervals. The PIM joinmessages can be active PIM joins since the PIM BDR is now the active DR.For example, the active PIM DR (e.g., the PIM BDR after migration) cansend periodic PIM join messages upstream. The active joins can propagateto other PIM routers, though in many cases such PIM joins may not makeany multicast state changes along the way as the complete multicast treewas already constructed in the previous steps.

In some aspects, the system, method, and non-transitorycomputer-readable medium described above can include receiving the PIMjoin message from the PIM BDR at the PIM router, which in this examplecan be a merge point; determining that the PIM router has previouslyreceived an active PIM join associated with the multicast group and hasan active multicast tree state (which can include the active multicasttree) associated with the multicast group, the active PIM join beingfrom an active PIM DR (as opposed to the PIM BDR prior to migration),setting the second instance of the backup multicast tree state (whichcan include the backup multicast tree) at the PIM router to a blockingstate; and sending, by the PIM router, the first unicast message to theaddress identified in the PIM join message from the PIM BDR (e.g., theaddress of the PIM BDR), the first unicast message indicating that thePIM router is the merge point between the active multicast tree and thebackup multicast tree.

In some aspects, the system, method, and non-transitorycomputer-readable medium described above can include receiving, by adifferent PIM router, an active PIM join associated with a second hostdevice and the multicast group, where the different PIM router is a newmerge point for the backup multicast tree and the active multicast treeand is located along a path between the source of the multicast trafficand both the second host device and the PIM BDR (e.g., a differentnetwork, such as a different LAN, than the PIM BDR, the PIM router, andthe active PIM DR); determining that the different PIM router haspreviously received the backup PIM join and has a third instance of thebackup multicast tree state associated with the multicast group; settingthe third instance of the backup multicast tree state to a blockingstate; sending, by the different PIM router, a third unicast message tothe address identified in the PIM join message from the PIM BDR (e.g.,the address of the PIM BDR), the third unicast message indicating thatthe different PIM router is the new merge point for the active multicasttree and the backup multicast tree; and sending, by the different PIMrouter, a copy of the active PIM join to the PIM router, the copy of theactive PIM join identifying an address associated with the different PIMrouter and identifying the different PIM router as the new merge point.This case may arise when a new active join is received on the backuppath before the merge point (e.g., the PIM router described above).

Moreover, in response to receiving the PIM join message sent by the PIMBDR, the PIM router can store the second instance of the backupmulticast tree state and a unicast address (e.g., the address of the PIMBDR) associated with a designated destination (e.g., the PIM BDR) forunicast communications relating to the backup multicast tree and/or theactive multicast tree. In response to receiving the active PIM join, thePIM router can also update the unicast address to the address of thedifferent PIM router and update the second instance of the backupmulticast tree state at the PIM router based on the active PIM join.

In some aspects, the system, method, and non-transitorycomputer-readable medium described above can include receiving, by thenext hop, the PIM join message from the PIM BDR; in response toreceiving the PIM join message, determining that the next hop does nothave multicast tree state associated with the multicast group and thesource of the multicast traffic; instantiating the multicast tree stateat the next hop; storing, by the next hop, the address associated withthe PIM BDR as a unicast address for communicating with the PIM BDR; andsending, by the next hop, a copy of the PIM join message towards the PIMrouter, the copy of the PIM join message identifying the addressassociated with the PIM BDR.

Example Embodiments

Disclosed are systems, methods, and computer-readable media forimplementing redundant multicast trees with fast recovery and without(or with limited) duplication of traffic. The present technologies willbe described in more detail in the following disclosure as follows. Thediscussion begins with a description of example models and architecturefor protocol independent multicast (PIM) services, as illustrated inFIGS. 1 through 2C. A description of example methods and processes forimplementing redundant multicast trees with faster recovery and without(or with limited) duplication of traffic, as illustrated in FIGS. 3Athrough 8, will then follow. The discussion concludes with a descriptionof an example network device, as illustrated in FIG. 9, and an examplecomputing device architecture, as illustrated in FIG. 10, includingexample hardware components suitable for performing networking andcomputing operations.

The disclosure now turns to FIG. 1, which illustrates an example model100 for PIM services. The example model 100 includes a source 112 ofmulticast traffic. The source 112 can be any computing device or nodesuch as, for example, a server, a virtual machine (VM), a softwarecontainer, a laptop computer, a smartphone, a tablet computer, a switch,a desktop computer, a network device, etc. The source 112 is illustratedsending (120) a data flow to a multicast group G including variousdevices or receivers that are members of the multicast group G.

If a device or node that is not a member of the multicast group G wantsto receive traffic from the source 112 to the multicast group G, thedevice or node can issue a membership request expressing interest injoining the multicast group G to receive such traffic from the source112 to the multicast group G. For example, host 102, which in thisexample is not currently a member of the multicast group G, can issue amembership request 122 expressing an interest in receiving traffic fromthe source 112 to the multicast group G. Host 102 can be any computingdevice or node such as, for example, a laptop computer, a smartphone, atablet computer, a gaming system, a smart television, a server, a VM, asoftware container, a network device, etc.

The host 102 can send the membership request 122 using anycommunications protocol or mechanism suitable for establishing multicastgroup memberships, such as Internet Group Management Protocol (IGMP),multicast listener discovery (MLD) protocol, etc. Moreover, the host 102can send the membership request 122 to a PIM designated router (DR) 104connected to the host 102 via a network 140 and/or to all PIM routers onthe network 140. The network 140 can be, for example, a private or localnetwork such as a local area network (LAN). The PIM DR 104 can be alocal PIM-capable router running as, or elected as, a designated routerfor receivers on the network 140. The PIM DR 104 is also the last hoprouter (LHR) for PIM traffic and operations associated with the host102. As a DR router, PIM DR 104 can act on behalf of hosts connected tothe DR (e.g., via a shared LAN) with respect to PIM operations andsignaling. Thus, in this example, PIM DR 104 can act on behalf of host102, which is connected to PIM DR 104 via network 140, with respect toPIM operations and signaling (e.g., PIM joins, PIM prunes, etc.).

For example, after receiving the membership request 122, PIM DR 104 cansend a PIM join message 124 towards the source 112 of the multicasttraffic to multicast group G. The PIM join message 124 in this examplecan be described as an (S, G) join (where S represents the source 112and G represents the multicast group G) because it joins multicast groupG for source S (112) to that group. The (S, G) join travels hop-by-hoptowards a merge point or rendezvous point (RP) for the multicast groupG, and each PIM-capable router that receives the (S, G) joininstantiates a multicast tree state for the multicast group G.Eventually, the (S, G) join reaches the merge point or RP that alreadyhas (S, G) join state for the multicast group G, and where join messagesfrom various receivers converge and form a multicast distribution treefor multicast group G that is rooted at the merge point or RP.

To illustrate, after receiving the membership request 122, PIM DR 104can send a PIM join message 124 to the next hop along the path to thesource 112, which in this example is PIM router 106 on network 150.Network 150 can include a private and/or public network, such as a LAN,a wide area network (WAN), etc. For example, network 150 can be a corenetwork or service provider network. PIM router 106 can receive the PIMjoin message 124, instantiate a multicast tree state for the multicastgroup G, and forward the PIM join message 124 to the next hop along thepath to the source 112, which in this example is PIM router 108. PIMrouter 108 can receive the PIM join message 124 and similarlyinstantiate a multicast tree state for the multicast group G and forwardthe PIM join message 124 to the next hop along the path to the source112, which in this example is first hop router (FHR) 110.

FHR 110 can be a PIM-capable router connected to the source 112. FHR 110can be connected to the source 112 via network 160, which can include aprivate or local network such as a LAN. Moreover, the FHR 110 in thisexample can represent a merge point used as the root of the multicastdistribution tree for multicast group G. However, in other examples, oneor more other PIM routers (on one or more same or different networks asFHR 110) can be a merge point or RP for multicast group G either in lieuof or in addition to FHR 110.

FHR 110 can receive the PIM join message 124 and instantiate (126) themulticast distribution tree for multicast group G. At this point, host102 is a member of the multicast group G and can receive traffic fromthe source 112 destined to the multicast group G. The traffic can berouted to the host 102 using the multicast distribution tree formulticast group G. For example, upon receiving a data flow from source112 destined to the multicast group G, FHR 110 forward (128) the flow toPIM router 108 based on the multicast distribution tree for multicastgroup G. PIM router 108 can receive the flow and forward (128) the flowto PIM router 106 using the multicast distribution tree for multicastgroup G. PIM router 106 can receive the flow and similarly use themulticast distribution tree for multicast group G to forward (128) theflow to the next hop towards the host 102, which in this example is PIMDR 104. PIM DR 104 can then receive the flow and forward (128) the flowto the host 102. In this way, the host 102 can receive the flow and anyfuture flows from the source 112 destined to the multicast group G untilthe host 102 leaves the multicast group G.

FIG. 2A illustrates an example PIM services deployment 200 with activeand backup designated routers in an example topology with disjointpaths. In this example, the PIM DR 104 operates as an active designatedrouter for host 102 and resides on an active path 202A to the source112, which is associated with an active multicast distribution tree, andPIM BDR 204 is a backup designated router (BDR) for host 102 residing ona backup path 202B to the source 112. The PIM BDR 204 can be deployed orelected as a backup DR for redundancy and used to establish a backupmulticast distribution tree which can become the active multicastdistribution tree if a problem or failure occurs with the PIM DR 104,the active multicast distribution tree, or any link or element in theactive path 202A. Each PIM router along the backup path 202B, includingPIM BDR 204, PIM routers 206 and 208, and FHR 210, can store the backupmulticast distribution tree state for potential use to recover from aproblem or failure that disrupts multicast traffic or PIM operationsover the active path 202A and active PIM DR 104.

For example, if a problem or failure that disrupts multicast traffic orPIM operations over the active path 202A and active PIM DR 104 isencountered, the active DR role can be migrated to the PIM BDR 204 andthe backup path 202B can become the active path for multicastcommunications associated with the multicast group G. As such, thebackup multicast distribution tree can be enabled for multicastcommunications and replace the previously active multicast distributiontree (associated with path 202A) as the new active multicastdistribution tree. To establish the backup multicast distribution treestate, the PIM BDR 204 is first set to backup designated router. The PIMBDR 204 then sends a PIM join message towards the source 112. In thejoin attributes of the PIM join message, the PIM BDR 204 can add itsaddress (e.g., its IP loopback address) to inform each hop what deviceis the originator of the PIM join message and allow other hops in thebackup path 202B to communicate with the PIM BDR 204 using unicastcommunications (e.g., via the address in the join attributes). The PIMBDR 204 can also add a flag in the PIM join message (e.g., as a joinattribute) indicating that the PIM join message is a backup PIM joinfrom a backup designated router. This flag thus informs other hops thatthe PIM join message is a backup PIM join and the PIM BDR 204 is abackup designated router.

In addition, the PIM BDR 204 sets its backup multicast distribution treestate (e.g., (S, G) state) in blocking or non-forwarding mode. Thebackup multicast distribution tree state is set to blocking ornon-forwarding mode because an active multicast distribution tree isalready available and in use, and to prevent triggering of PIM assertmessages if there are any PIM routers that do not understand the backupPIM join and start forwarding traffic on the backup multicastdistribution tree. Moreover, if the PIM BDR 204 continuously receivestraffic on the backup multicast distribution tree for a threshold PIMjoin interval (e.g., 3 PIM join intervals), the PIM BDR 204 can log suchevent and/or an indication that a PIM router is present which does notunderstand the backup PIM join.

When the next hop, PIM router 206, receives the backup PIM join from PIMBDR 204, it checks if it already has active state for the multicastgroup G (e.g., (S,G) state). Since at this point the PIM router 206 doesnot have any active state for the multicast group G, it creates an entry(e.g., (S,G) entry) for the multicast group G, stores the originatoraddress included by the PIM BDR 204 in the backup PIM join (e.g., aspart of a join attribute), and forwards the backup PIM join to the nexthop, which in this example is PIM router 208. In some cases, aspreviously explained, if the PIM router 206 receives backup PIM joinsfrom different PIM routers for a same multicast group (e.g., (S, G), thePIM router 206 can add the addresses of the PIM BDRs that originatedsuch backup PIM joins (e.g., which can be obtained from BDR valuescontained in the backup PIM joins), and forward a backup PIM joincontaining the addresses of the PIM BDRs to the next hop as describedherein.

When the backup PIM join reaches the next hop, PIM router 208, the PIMrouter 208 can similarly check that it does not already have activestate for the multicast group G (e.g., (S,G) state), create an entry(e.g., (S,G) entry) for the multicast group G, store the addressesincluded by the PIM BDR 204 and the PIM router 206 in the backup PIMjoin (e.g., as part of a join attribute), and forward the backup PIMjoin to the next hop, which in this example is FHR 210.

When the backup join reaches FHR 210, the FHR 210 can store theaddresses of the PIN BDR 204 and the PIM routers 206 and 208 included inthe backup PIM join message (e.g., as join attributes) for use in futureunicast communications with any of such routers. In this exampletopology with disjoint paths and two FHRs (110, 210), the FHR 210 canalso act as a merge point since it is a first hop router, and send aunicast message to the address of the PIM BDR 204, which the FHR 210 canobtain from the backup PIM join message. In the unicast message, the FHR210 can include (e.g., in the header as part of the unicast message) itsown address to allow the PIM BDR 204 to obtain the address of the FHR210 for future unicast communications and PIM signaling, such asdesignated router and backup multicast distribution tree migrations, tothe FHR 210. This can allow the PIM BDR 204 and FHR 210 to usepoint-to-point signaling for PIM migration operations and communicationsas opposed to hop-by-hop signaling, thus eliminating or reducingduplicate traffic for such PIM migration operations and communications.

In other cases where the FHR 210 is actually a merge point (for exampleif FHR 210 was instead a fork point for both the active and backup paths202A and 202B), when the backup PIM join reaches the FHR 210, the FHR210 would see an active join state already present and set the outgoinginterface (OF) of the backup PIM join to blocking or non-forwardingmode. The FHR 210 would also send a unicast message to the PIM BDR 204as previously explained. Moreover, in both scenarios, the FHR 210 cansend multiple unicast packets to the PIM BDR 204 to prevent or reducethe likelihood of a packet loss from impacting the process.

When the PIM BDR 204 receives the unicast message from the FHR 210, itstores the address of the FHR 210, which the PIM BDR 204 can obtain fromthe unicast message, and can also store the route from the FHR 210 tothe PIM BDR 204. As previously explained, the address of the FHR 210 canbe used by the PIM BDR 204 to send a unicast message to the FHR 210 whenthere is a migration of the PIM BDR 204 from backup to active designatedrouter. For example, upon detecting a DR migration triggering event suchas a link failure or an active PIM DR (e.g., 104) failure, the PIM BDR204 can migrate or switch to active DR and take over active DRoperations. Here, the PIM BDR 204 can make its backup multicastdistribution tree state active by updating the backup multicastdistribution tree state from blocking to forwarding mode. The PIM BDR204 can also send a unicast message to the FHR 210 (using the address ofthe FHR 210 obtained from the unicast message received by the PIM BDR204 from the FHR 210) instructing the FHR 210 to similarly update thebackup multicast distribution tree state from blocking to forwarding. Insome cases, the PIM BDR 204 can send such unicast message multiple timesin case there is a packet loss. The FHR 210 can then start forwardingmulticast traffic using the newly active multicast distribution tree.

This procedure allows such migration and processing to be performed atonly 2 nodes (e.g., the PIM BDR 204 and FHR 210) using point-to-pointsignaling as opposed to hop-by-hop signaling, thus reducing oreliminating duplicate traffic otherwise resulting from hop-by-hopsignaling. Such reduction in traffic used to perform such migrations andprocessing can significantly reduce the burden on, and performance of,the network and reduce the time it takes to complete a designated routermigration.

In some cases, when the PIM BDR 204 becomes the active DR, it not onlysends a unicast message to the FHR 210 to change the backup multicastdistribution tree state from blocking to forwarding, but it also canstart sending active PIM joins. Further, in some cases, even thoughperiodic active PIM joins will start propagating from the PIM BDR 204,such PIM joins may not necessarily make changes to the multicastdistribution tree state along the path since the complete multicastdistribution tree has been previously constructed.

FIG. 2B illustrates an example PIM services deployment 230 with activeand backup designated routers in an example topology with a merged path.A topology with a merged path can result when at least one router ispart of both the active path 202A to the source 112 and the backup path202B to the source 112. In this example, PIM router 240 is part of boththe active path 202A and the backup path 202B, and thus represents afork or merge point in a merged path (e.g., a merge point for the backupmulticast distribution tree and the active multicast distribution tree).

In the example PIM services deployment 230, when the PIM BDR 204 sends abackup PIM join message towards the source 112, the PIM join messagewill traverse each hop along the backup path 202B, as previouslydescribed with respect to FIG. 2A. However, in this example, when thebackup PIM join message reaches PIM router 240 (e.g., the fork or mergepoint), PIM router 240 will detect that there is already an active PIMjoin, which was originated from PIM DR 104 over the active path 202A.Accordingly, the backup PIM join will stop at PIM router 240 rather thancontinuing to the FHR 110. The PIM router 240 can obtain and store theaddresses of the PIM BDR 204 and the PIM router 206, which can beincluded in the backup PIM join message (e.g., as join attributes), foruse in future unicast communications with any of such routers and canset the outgoing interface (OIF) of the backup PIM join to blocking ornon-forwarding mode.

The PIM router 240 can then send a unicast message to the address of thePIM BDR 204. The unicast message can include (e.g., in the header aspart of the unicast message) an address of the PIM router 240 to allowthe PIM BDR 204 to obtain the address of the PIM router 240 for futureunicast communications and PIM signaling to PIM router 240, such asdesignated router and backup multicast distribution tree migrations. Theunicast message can also include an indication informing the PIM BDR 204that the PIM router 240 is a fork or merge point. Upon a failuretriggering a designated router migration from PIM DR 104 to PIM BDR 204,the PIM BDR 204 can use the address of the PIM router 240 to send aunicast packet to the PIM router 240 instructing the PIM router 240 toupdate the backup multicast distribution tree state associated with thePIM BDR 204 and backup path 202B from blocking to forwarding. In thisway, the PIM BDR 204 and the PIM router 240 can use point-to-pointunicast communications with each other to perform a designated routermigration, thereby eliminating or reducing duplicate traffic for suchPIM migration operations and communications.

FIG. 2C illustrates an example PIM services deployment 250 with activeand backup designated routers in an example topology with a merged pathand a different network 260 (e.g., a different LAN) that overlaps with acurrent backup multicast distribution tree. As illustrated in thisexample, the different network 260 includes a different path 258 to thesource 112, which merges with the backup path 202B. The different path258 and the backup path 202B here merge at PIM router 206 on the backuppath 202B.

The different network 260 includes host 252, PIM DR 254, and PIM router256. When host 252 wants to join the multicast distribution groupassociated with the source 112, PIM DR 254 can send an active PIM jointowards the source 112. The PIM DR 254 can send the active PIM join overthe different path 258, which subsequently can be received and processedby the next hop, the PIM router 256. The PIM router 256 can then forwardthe active PIM join to the next hop, which in this case is PIM router206 on the backup path 202B.

In this example, a new active PIM join is received on the backup path202B before the fork or merge point (e.g., PIM router 240) between thebackup path 202B and the active path 202A. In such scenarios, it may notbe guaranteed that the active PIM join from the different path 258 willreach the fork or merge point (e.g., PIM router 240) before a backup PIMjoin transmitted by the PIM BDR 204 over the backup path 202B. Forexample, in some cases, the PIM router 240 may receive the backup PIMjoin from PIM BDR 204 before the new active PIM join from PIM DR 254 onthe different network 260. In such examples, upon receiving the backupPIM join, the PIM router 240 may process and forward the backup PIM jointowards the source 112, and receive the new active PIM join at a latertime.

To prevent potential issues resulting from the backup PIM join reachinga fork or merge point before the active PIM join, a mechanism can beimplemented to process new active PIM joins received on a backup path(202B) as follows. When the PIM DR 254 originates a new active PIM joinfor host 252, it can forward the new active PIM join to the next hop,which in this case is PIM router 256 on the different network 260. ThePIM router 256 can receive the new active PIM join and create an activemulticast distribution tree state based on the new active PIM join. ThePIM router 256 can then forward the new active PIM join to the next hop,which in this case is PIM router 206 on the backup path 202B.

When the PIM router 206 receives the new active PIM join, it candetermine that it previously received a backup PIM join for the samemulticast group and source (e.g., multicast group (S, G)). In responseto determining that a backup PIM join was already received, the PIMrouter 206 can send a unicast message to the originator of the backupPIM join, which in this example is PIM BDR 204, and forward the newactive PIM join to PIM router 240. The PIM router 206 can send theunicast message using an address of the PIM BDR 204 obtained from thebackup PIM join message as previously explained. The unicast message tothe PIM BDR 204 can inform the PIM BDR 204 that the PIM router 206 isnow a fork or merge point for the backup multicast distribution tree.

The PIM BDR 204 can receive the unicast message from the PIM router 206,and update an entry for the multicast group (e.g., (S,G)) to include theaddress of the PIM router 206 and an indication that the PIM router 206is a new fork or merge point between the backup path 202B and thedifferent path 258. Each hop after the PIM router 206 can continue usingthe active multicast distribution tree state as its active state.

The multicast technologies described above with respect to FIGS. 2A-2Ccan handle various types of failures to reduce or eliminate downtimethat may result from such failures and increase the time of convergence.For example, the technologies herein can provide PIM core (e.g., network150) isolation on the current PIM DR 104. To illustrate, with referenceto FIG. 2A, if interface or link between PIM DR 104 and PIM router 106fails or experiences a problem, such failure may not lead to adesignated router re-election, as the network 140 (e.g., shared LANsegment) would still be active or functional. A new designated routerfor the network 140 and/or host 102 would thus be unnecessary and thePIM DR 104 could continue as the designated router for the network 140and/or host 102.

In some deployments, PIM core isolation may be handled by script, whichmay cause the access interface or link (e.g., the interface or linkbetween the PIM DR 104 and the host 102) to also go down. However, insuch scenarios, a regular designated router re-election procedure can betriggered, and the implementations herein can still provide fasterconvergence of multicast services than other multicast servicesimplementations. Moreover, when unicast reachability on the active path202A changes, active PIM joins from PIM DR 104 could instead beoriginated from the backup path 202B. For example, active PIM joins fromPIM DR 104 can be transmitted to the PIM BDR 204 and forwarded by thePIM BDR 204 along the backup path 202B. When the PIM BDR 204 receivesthe active PIM join associated with the PIM DR 104, it can notify thefork or merge point (e.g., 110 or 240) to start forwarding traffic usingthe backup multicast distribution tree state. In this scenario,multicast services would still resume quickly.

In another example, the technologies herein can also handle failuresexperienced in deployments having a ring topology. To illustrate, assumethe network 140 (e.g., the shared LAN) has a ring topology. Here, whenthere is node failure which causes the ring to break, the PIM DR 104 andthe PIM BDR 204 can both act as the designated router on the network 140and start forwarding traffic right away.

In yet another example, when the PIM DR 104 goes down or experiences afailure, the PIM BDR 204 can detect the failure and perform a designatedrouter migration as previously explained. Thus, upon detecting thefailure, the PIM BDR 204 can take over right away as the designatedrouter and start forwarding traffic.

The technologies herein can also handle PIM any-source multicast (ASM)and PIM rendezvous point tree (RPT) switchover. For example, in someimplementations, the technologies herein can implement a sourcediscovery mechanism, such as the source discovery mechanism described inRequest for Comments (RFC) 8364 (ISSN 2070-1721) by Wijnands el al.,entitled “PIM Flooding Mechanism (PFM) and Source Discovery (SD)” anddated March 2018, the contents of which are incorporated herein byreference in their entirety. In such examples, the PIM DR 104 and thePIM BDR 204 would both know about the source 112 and can opt to send PIMjoins for the multicast group (e.g., (S,G)) directly towards the source112.

In other implementations, if a source discovery mechanism is not used oravailable, there may be cases where the PIM DR 104 becomes theshortest-path tree (SPT) after receiving source traffic, where the PIMBDR 204 is still creating the backup multicast distribution tree to therendezvous point (RP). The RP can be or act as the fork or merge pointin this example. In this case, the backup multicast distribution treewould be setup until the RP. When the PIM DR 104 fails, the PIM BDR 204can start receiving traffic from the shared tree (e.g., the RP Tree) andcan later (optionally) move to the SPT. Since a backup path (202B) canbe setup (as previously explained) in advance, convergence would stillbe very fast.

In addition, the technologies herein can provide interoperability withnetworks where some of the PIM routers do not support the backupdesignated router implementation or features herein. Thus, thetechnologies herein can be implemented without backwards compatibilityissues even if a network has any PIM routers that do not support some orall of the mechanisms or features herein. For example, if a PIM routerin the PIM core (e.g., network 150) does not support or understand thebackup multicast distribution tree technologies herein (e.g., thecreation and/or use of a backup multicast distribution tree as describedherein), the PIM router may treat a backup PIM join as an active PIMjoin and could potentially start sending traffic towards the PIM BDR204. However, if the PIM BDR 204 starts receiving the multicast traffic,it can drop such traffic. In some implementations, the PIM BDR 204 canstop sending backup PIM joins after a period of time. For example, atimer can be used to determine if the backup multicast distribution treehas continuously received traffic over the course of n number of PIMjoin intervals.

FIG. 3A illustrates an example flow 300 for processing active PIM joins(e.g., active (S, G) joins) associated with a multicast group (G) andsource 112 (S). For illustrative and explanation purposes, the flow 300in this example is described with reference to the deployment 200 shownin FIG. 2A.

At step 302, PIM DR 104 receives from the host 102 a multicast groupmembership (S, G) associated with the multicast group G and source 112.The membership request can be a transmitted by the host 102 using theInternet Group Management Protocol (IGMP) or any other suitablecommunications protocol. The membership request can indicate that thehost 102 is interested in receiving multicast traffic associated withmulticast group G from source 112.

At step 304, the PIM DR 104 can instantiate forwarding state and beginforwarding traffic on the network 140 (e.g., the LAN) associated withthe host 102 and the PIM DR 104. At step 306, the PIM DR 104 can send anactive PIM join to PIM router 106 on the active path 202A.

At step 308, the PIM router 106 can receive the active PIM join andinstantiate forwarding state for the active multicast distribution treeassociated with the active PIM join. At step 310, the PIM router 106 canforward the active PIM join to the PIM router 108.

At step 312, the PIM router 108 can receive the active PIM join andinstantiate forwarding state for the active multicast distribution treeassociated with the active PIM join. At step 314, the PIM router 108 canforward the active PIM join to the FHR 110.

At step 316, the FHR 110 can receive the active PIM join and instantiateforwarding state for the active multicast distribution tree associatedwith the active PIM join. At this point, the full active multicastdistribution tree has been created for the active path 202A andmulticast traffic can be forwarded using the active multicastdistribution tree.

FIG. 3B illustrates an example flow 330 for processing backup PIM joins(e.g., backup (S, G) joins) associated with a multicast group (G) andsource 112 (S). For illustrative and explanation purposes, the flow 330in this example is described with reference to the deployment 200 shownin FIG. 2A.

At step 332, PIM BDR 204 receives from the host 102 a multicast groupmembership request (S, G) associated with the multicast group G andsource 112. At step 334, the PIM BDR 204 receives the membership requestand subsequently instantiates backup multicast tree state and sets thebackup multicast tree to blocking or non-forwarding. At step 336, thePIM BDR 204 sends a backup PIM join to PIM router 206 on the backup path202B.

At step 338, the PIM router 206 receives the backup PIM join andinstantiates the backup multicast tree state associated with the backupPIM join. At step 340, the PIM router 206 forwards the backup PIM jointo the PIM router 208.

At step 342, the PIM router 208 receives the backup PIM join andinstantiates the backup multicast tree state associated with the backupPIM join. At step 344, the PIM router 208 forwards the backup PIM jointo the FHR 210.

At step 346, the FIR 210 can receive the backup PIM join and set theoutgoing interface (OIF) of the backup PIM join to blocking state. Atstep 348, the FHR 210 also instantiates the backup multicast tree stateassociated with the backup PIM join. At this point, the full backupmulticast tree has been created for the backup path 202B.

At step 350, the FHR 210 sends to the PIM BDR 204 a unicast messageincluding an address (e.g., a loopback IP address) of the FHR 210. Theaddress of the FHR 210 can be included as part of the unicast message(e.g., in the header). At step 352, the PIM BDR 204 receives the unicastmessage, and stores the address of the FHR 210 in the unicast messageand the route traversed by the unicast message from the FHR 210 to thePIM BDR 204. At this point, the PIM BDR 204 has an address it can use tosend unicast communications to the FHR 210 in order to perform PIMoperations such as a designated router migration as described herein.Similarly, the FHR 210 has the address of the PIM BDR 204 (e.g.,included in the backup PIM join message), which the FHR 210 can also useto send unicast communications to the PIM BDR 204. Moreover, the PIM BDR204 knows from the route of the unicast message each of the hops alongthe backup path 202B.

FIG. 3C illustrates an example flow 360 for performing a designatedrouter migration. For illustrative and explanation purposes, the flow360 in this example is described with reference to the deployment 200shown in FIG. 2A.

At step 362, PIM BDR 204 detects a DR migration trigger. The DRmigration trigger can be any condition, activity or event configured totrigger the migration of the DR role and/or active multicast tree statefrom the active PIM DR 104 to a backup or standby PIM DR (e.g., PIM BDR204). For example, the DR migration trigger can be an access interfacefailure (e.g., an access interface going down), a core link failure, afailure experienced by one or more PIM routers (e.g., one or more PIMrouters going down), and/or any other event or condition that mayinterfere with or cause errors or disruption with multicast routing andcommunications using a currently-active path and/or PIM DR (e.g., 104).The DR migration trigger can thus trigger migration of DR roles andmulticast tree states (e.g., from an active to a backup multicast treestate and vice versa).

At step 364, upon detecting the DR migration trigger, the PIM BDR 204can change its state from blocking to forwarding, which allows thebackup multicast tree hosted by the PIM BDR 204 to become active forrouting associated multicast traffic. At step 366, the PIM BDR 204 sendsa unicast message to the FHR 210, instructing the FHR 210 to startforwarding traffic using the backup multicast tree (which has since beenmigrated from backup to active). In some cases, the PIM BDR 204 can sendmultiple unicast messages to the FHR 210 in case of packet loss in thenetwork. Moreover, in some cases, upon becoming the active PIM DR, inaddition to sending the unicast message to the FHR 210, the PIM BDR 204can also start sending active PIM join messages.

At step 368, upon receiving the unicast message from the PIM BDR 204,the FHR 210 updates its state (e.g., the backup multicast tree state)from blocking to forwarding. At this point, the FHR 210 can startforwarding traffic using the backup multicast tree that has been set asthe active tree and enabled for forwarding.

At step 370, the PIM BDR 204 can send active PIM joins, which will startpropagating from the PIM BDR 204. At step 372, the PIM router 206receives the active PIM joins from the PIM BDR 204, processes them, andforwards them to the next hop (e.g., PIM router 208). At step 374, thePIM router 208 similarly receives the active PIM joins, processes them,and forwards them to the next hop (e.g., FHR 210).

FIG. 4A illustrates an example flow 400 for processing backup PIM joins(e.g., backup (S, G) joins) associated with a multicast group (G) andsource 112 (S) in an example topology with a merged path. Forillustrative and explanation purposes, the flow 400 in this example isdescribed with reference to the deployment 230 shown in FIG. 2B, whichincludes a topology with a merged path.

At step 402, PIM BDR 204 receives from the host 102 (e.g., throughbackup path 202B) a multicast group membership request (S, G) associatedwith the multicast group G and source 112. At step 402, the PIM BDR 204receives the membership request and instantiates backup multicast treestate and sets the backup multicast tree to blocking or non-forwarding.At step 406, the PIM BDR 204 sends a backup PIM join to PIM router 206on the backup path 202B.

At step 408, the PIM router 206 receives the backup PIM join andinstantiates the backup multicast tree state associated with the backupPIM join. At step 410, the PIM router 206 forwards the backup PIM jointo the PIM router 208.

At step 412, the PIM router 240 (e.g., the merge point) receives thebackup PIM join, instantiates the backup multicast tree state associatedwith the backup PIM join, and sets the OIF of the backup PIM join toblocking state. At step 414, the PIM router 240 then sends a unicastmessage, which includes an address (e.g., a loopback IP address) of thePIM router 240, to PIM BDR 204. The address of the PIM router 240 can beincluded as part of the unicast message (e.g., in the header).

At step 416, the PIM BDR 204 receives the unicast message, and storesthe address of the PIM router 240 in the unicast message and the routetraversed by the unicast message from the PIM router 240 to the PIM BDR204. At this point, the PIM BDR 204 has an address it can use to sendunicast communications to the merge point (e.g., PIM router 240) inorder to perform PIM operations such as a designated router migration asdescribed herein. Similarly, the PIM router 240 has the address of thePIM BDR 204 (e.g., included in the backup PIM join message), which thePIM router 240 can also use to send unicast communications to the PIMBDR 204. Moreover, the PIM BDR 204 knows from the route of the unicastmessage each of the hops along the backup path 202B.

FIG. 41B illustrates an example flow 430 for performing a designatedrouter migration in an example topology with a merged path. Forillustrative and explanation purposes, the flow 430 in this example isdescribed with reference to the deployment 230 shown in FIG. 2B, whichincludes a topology with a merged path.

At step 432, PIM BDR 204 detects a DR migration trigger that initiatesthe DR migration. The DR migration trigger can be any condition,activity or event configured to trigger the migration of the DR roleand/or active multicast tree state from the active PIM DR 104 to abackup or standby PIM DR (e.g., PIM BDR 204). For example, the DRmigration trigger can be an access interface failure (e.g., an accessinterface going down), a core link failure, a failure experienced by oneor more PIM routers (e.g., one or more PIM routers going down), and/orany other event or condition that may interfere with or cause errors ordisruption with multicast routing and communications using acurrently-active path and/or PIM DR (e.g., 104). The DR migrationtrigger can thus trigger migration of DR roles and multicast tree states(e.g., from an active to a backup multicast tree state and vice versa).

At step 434, upon detecting the DR migration trigger, the PIM BDR 204can change its state from blocking to forwarding, which allows thebackup multicast tree hosted by the PIM BDR 204 to become active forrouting associated multicast traffic. At step 436, the PIM BDR 204 sendsa unicast message to the merge point, PIM router 240. The unicastmessage can instruct the PIM router 240 to start forwarding trafficusing the backup multicast tree (which has since been migrated frombackup to active). The unicast message can include an address of the PIMBDR 204. The address of the PIM BDR 204 can be included as part of theunicast message (e.g., in the header of the unicast message). In somecases, the PIM BDR 204 can send multiple unicast messages to the PIMrouter 240 in case of packet loss in the network.

At step 438, upon receiving the unicast message from the PIM BDR 204,the PIM router 240 updates its state (e.g., the backup multicast treestate) from blocking to forwarding. At this point, the PIM router 240can start forwarding traffic using the backup multicast tree that hasbeen set as the active tree and enabled for forwarding.

At step 440, the PIM BDR 204 can send active PIM joins, which will startpropagating from the PIM BDR 204. At step 442, the PIM router 206receives the active PIM joins from the PIM BDR 204, processes them, andforwards them to the next hop (e.g., PIM router 240). The PIM router 240can receive the active PIM joins from the PIM router 206 and similarlyprocess them.

FIG. 5 illustrates an example flow 500 for processing active PIM joins(e.g., active (S, G) joins) associated with a multicast group (G) andsource 112 (S) in an example topology with a merged path and a networkthat overlaps with a current backup multicast distribution tree. Forillustrative and explanation purposes, the flow 500 in this example isdescribed with reference to the deployment 250 shown in FIG. 2C.

At step 502, PIM DR 254 (in the overlapping network 260) receives fromhost 252 a multicast group membership (S, G) associated with themulticast group G and source 112. The membership request can be atransmitted by the host 252 using IGMP or any other suitablecommunications protocol. The membership request can indicate that thehost 252 is interested in receiving multicast traffic associated withmulticast group G from source 112.

At step 504, the PIM DR 254 can instantiate the multicast tree state. Atstep 506, the PIM DR 254 can send an active PIM join to PIM router 256on path 258.

At step 508, the PIM router 206 can receive the active PIM join anddetect an existing backup PIM join for the same multicast group (e.g.,(S, G)). The existing backup PIM join can be a backup PIM joinpreviously received by the PIM router 206 from the PIM BDR 204.

In response to detecting the existing backup PIM join for the samemulticast group, at step 510, the PIM router 206 can send a unicastmessage to the backup PIM join originator (e.g., PIM BDR 204),indicating that the PIM router 206 is a fork or merge point for thebackup multicast tree. At step 512, the PIM router 206 can also send anactive PIM join to PIM router 240, which is also a merge point for theactive path 202A and the backup path 202B.

Based on the unicast message from PIM router 206, at step 514, the PIMBDR 204 can then update its fork point entry to include the address ofthe PIM router 206, which is now a fork point for path 258 and backuppath 202B. Each hop after PIM router 206 can continue making its stateto the active multicast tree.

Having described example systems and concepts, the disclosure now turnsto the methods illustrated in FIGS. 6, 7, and 8. The steps outlinedherein are examples and can be implemented in any combination thereof,including combinations that exclude, add, or modify certain steps.

FIG. 6 illustrates an example method 600 for establishing an active PIMDR (e.g., PIM BDR 104), an active multicast tree state, and an activemulticast path (e.g., 202A). In this example, at step 602, the method600 includes receiving, by a PIM DR (104), a request (302) from a hostdevice (102) to join a multicast group (e.g., (S, G)) associated with asource (112) of multicast traffic.

In response to the request (302), at step 604, the method 600 caninclude sending, by the PIM DR (104), an active PIM join message (306)to a next hop (e.g., PIM router 106) between the PIM DR (104) and thesource (112) of multicast traffic (or a merge point). At step 606, thePIM DR (104) can also instantiate an active multicast tree state for themulticast group. Moreover, at step 608, the PIM DR (104) can send one ormore (or periodic) PIM hello messages to one or more devices on the PIMDR's network (e.g., 140) or shared LAN. The PIM DR (104) can use hellomessages to detect other PIM routers.

Hello messages can be sent periodically on each PIM enabled interface.In some cases, hello messages can be multicast to the ALL-PIM-ROUTERSgroup. When PIM is enabled on an interface or when a router firststarts, a Hello Timer (HT) is set to a value between 0 and a hello delay(e.g., Triggered Hello_Delay). This can prevent synchronization of hellomessages if multiple routers are powered on simultaneously. After theinitial hello message, a hello message can be sent periodically (e.g.,every Hello_Period). A hello timer can be used to trigger sending hellomessages on active interfaces.

At step 610, the method 600 can include sending, by the PIM DR (104),one or more PIM join messages towards the source (112) of the multicasttraffic (e.g., upstream). In some cases, the PIM DR (104) can sendperiodic PIM join messages upstream.

FIG. 7 illustrates an example method 700 for establishing a backup PIMDR (e.g., PIM BDR 204) and backup multicast path (e.g., 202B), andperforming a DR migration. In this example, at step 702, the method 700includes receiving, by a PIM BDR (204), a request (332) from a hostdevice (102) to join a multicast group (e.g., (S, G)) associated with asource (112) of multicast traffic.

At step 704, the method 700 can include, in response to the request(332), sending, by the PIM BDR (204), a PIM join message (e.g., backupPIM join 336) to a next hop (e.g., PIM router 206) between the PIM BDR(204) and the source (112) of multicast traffic. The PIM join message(e.g., backup PIM join 336) can include attributes identifying anaddress of the PIM BDR (204) and indicating that the PIM join message isa backup PIM join from a backup designated router.

At step 706, the method 700 can include receiving, by the PIM BDR (204),from a PIM router (e.g., FHR 210) located along a path (e.g., 202B)between the PIM BDR (204) and the source (112) of multicast traffic, aunicast message sent to the address of the PIM BDR (204). The unicastmessage can identify an address of the PIM router (e.g., FHR 210). ThePIM router (e.g., FHR 210) can use the address included in the PIM joinmessage sent by the PIM BDR (204) at step 704 and received by the PIMrouter (e.g., FHR 210). Since the PIM BDR (204) and the PIM router(e.g., FHR 210), which can be a merge point or a first hop router, haveeach others' addresses, they can communicate using unicast messaging toexchange any PIM-related information.

At step 708, the method 700 can include storing, by the PIM BDR (104),the address of the PIM router (e.g., FHR 210) and a route associatedwith the unicast message from the PIM router (e.g., FHR 210) to the PIMBDR (104).

At step 710, the method 700 can include, in response to a designatedrouter migration triggering event, changing an instance of a backupmulticast tree state at the PIM BDR (104) from blocking to forwarding.The backup multicast tree state can include the backup multicast treeassociated with the source (112) of multicast traffic and the multicastgroup (e.g., (S, G)). For example, when the PIM BDR (104) detects a DRmigration trigger, as previously explained, it can change its state toforwarding in order to activate and use the backup multicast tree forsubsequent multicast traffic associated with the multicast group.

At step 712, the method 700 can include sending, by the PIM BDR (204) tothe PIM router (e.g., FHR 210), a unicast message including aninstruction to change an instance of the backup multicast tree state atthe PIM router (e.g., FHR 210) from blocking to forwarding. The PIM BDR(204) can send the unicast message using the PIM router's addressobtained from the PIM router at step 706. When the PIM router (e.g., FHR210) receives the unicast message sent by the PIN BDR (204) in step 712,the PIM router can update its state (e.g., the backup multicast treestate) to forwarding mode and subsequently begin actively using thestate to forward multicast traffic associated with the multicast group.

FIG. 8 illustrates a flowchart of an example method 800 for processingPIM join messages and performing a DR migration at a merge point (e.g.,PIM router 240 in deployment 230, PIM router 206 in deployment 250) in aPIM deployment (e.g., 230, 250). In this example, at step 802, themethod 800 can include receiving, by a PIM router (e.g., 240, 206) at amerge point between an active multicast path (e.g., 202A) associatedwith a multicast group (e.g., (S, G)) and a backup multicast path (e.g.,202B) associated with the multicast group, a PIM join message (e.g.,410) from a PIM BDR (104). The PIM join message can identify an addressof the PIM BDR (204) and can indicate that the PIM join message is for abackup PIM join.

At step 804, the method 800 can include determining whether an activemulticast tree state already exists at the PIM router (e.g., 240, 206).If an active multicast tree state already does exist at the PIM router,at step 806, the method 800 can include instantiating at the PIM router(e.g., 240, 206) a backup multicast tree state associated with themulticast group and the source of the multicast traffic (e.g., (S, G)).Once the backup multicast tree state has been instantiated at the PIMrouter (e.g., 240, 206), the method 800 can proceed to step 812described below.

If, on the other hand, the method 800 at step 804 determines that anactive multicast tree state does not exist at the PIM router, the method800 proceeds to step 808, which can include setting the OIF of thebackup PIM join (e.g., the PIM join message received at step 802 fromthe PIM BDR) to a blocking state.

At step 810, the method 800 can include sending (e.g., by the PIMrouter) to the address of the PIM BDR (204) identified in the PIM joinmessage (e.g., 410), a unicast message including an address of the PIMrouter (e.g., 240, 206). The address in the unicast message will allowthe PIM BDR (204) to send unicast messages to the PIM router (e.g., 240,206).

At step 812, the method 800 can include receiving, at the PIM router(e.g., 240, 206) and from the PIM BDR (204), a unicast messageinstructing the PIM router (e.g., 240, 206) to update a backup multicasttree state to forwarding mode. The unicast message can be sent using theaddress included in the unicast message sent at step 810. Moreover, theinstruction to update a backup multicast tree state to forwarding modecan be in response to a DR migration event which triggers migration ofthe PIM BDR (204) and the backup multicast path (202B) from backup toactive. Thus, updating the backup multicast tree state to forwardingmode will allow the PIM router (e.g., 240, 206) to activate and use thebackup multicast tree state to forward associated multicast traffic.

At step 814, the method 800 can include updating, by the PIM router(e.g., 240, 206), the backup multicast tree state to forwarding mode.The PIM router (e.g., 240, 206) can update the backup multicast treestate to forwarding mode in response to the unicast message at step 812instructing the PIM router (e.g., 240, 206) to update the backupmulticast tree state to forwarding mode. At step 816, the method 800 caninclude forwarding multicast traffic associated with the multicast group(e.g., (S, G)) using the backup multicast tree state.

The disclosure now turns to FIGS. 9 and 10, which illustrate examplenetwork devices and computing devices, such as switches, routers, clientdevices, endpoints, servers, and so forth.

FIG. 9 illustrates an example network device 900 suitable forimplementing PIM routing and performing switching, routing, and othernetworking operations. Network device 900 includes a central processingunit (CPU) 904, interfaces 902, and a connection 910 (e.g., a PCI bus).When acting under the control of appropriate software or firmware, theCPU 904 is responsible for executing packet management, error detection,and/or routing functions. The CPU 904 preferably accomplishes all thesefunctions under the control of software including an operating systemand any appropriate applications software. CPU 904 may include one ormore processors 908, such as a processor from the INTEL X96 family ofmicroprocessors. In some cases, processor 908 can be specially designedhardware for controlling the operations of network device 900. In somecases, a memory 906 (e.g., non-volatile RAM, ROM, etc.) also forms partof CPU 904. However, there are many different ways in which memory couldbe coupled to the system.

The interfaces 902 are typically provided as modular interface cards(sometimes referred to as “line cards”). Generally, they control thesending and receiving of data packets over the network and sometimessupport other peripherals used with the network device 900. Among theinterfaces that may be provided are Ethernet interfaces, frame relayinterfaces, cable interfaces, DSL interfaces, token ring interfaces, andthe like. In addition, various very high-speed interfaces may beprovided such as fast token ring interfaces, wireless interfaces,Ethernet interfaces, Gigabit Ethernet interfaces, ATM interfaces, HSSIinterfaces, POS interfaces, FDDI interfaces, WIFI interfaces, 3G/4G/5Gcellular interfaces, CAN BUS, LoRA, and the like. Generally, theseinterfaces may include ports appropriate for communication with theappropriate media. In some cases, they may also include an independentprocessor and, in some instances, volatile RAM. The independentprocessors may control such communications intensive tasks as packetswitching, media control, signal processing, crypto processing, andmanagement. By providing separate processors for the communicationsintensive tasks, these interfaces allow the master microprocessor 904 toefficiently perform routing computations, network diagnostics, securityfunctions, etc.

Although the system shown in FIG. 9 is one specific network device ofthe present technologies, it is by no means the only network devicearchitecture on which the present technologies can be implemented. Forexample, an architecture having a single processor that handlescommunications as well as routing computations, etc., is often used.Further, other types of interfaces and media could also be used with thenetwork device 900.

Regardless of the network device's configuration, it may employ one ormore memories or memory modules (including memory 906) configured tostore program instructions for the general-purpose network operationsand mechanisms for roaming, route optimization and routing functionsdescribed herein. The program instructions may control the operation ofan operating system and/or one or more applications, for example. Thememory or memories may also be configured to store tables such asmobility binding, registration, and association tables, etc. Memory 906could also hold various software containers and virtualized executionenvironments and data.

The network device 900 can also include an application-specificintegrated circuit (ASIC) 912, which can be configured to performrouting and/or switching operations. The ASIC 912 can communicate withother components in the network device 900 via the connection 910, toexchange data and signals and coordinate various types of operations bythe network device 900, such as routing, switching, and/or data storageoperations, for example.

FIG. 10 illustrates a computing system architecture 1000 wherein thecomponents of the system are in electrical communication with each otherusing a connection 1005, such as a bus. Exemplary system 1000 includes aprocessing unit (CPU or processor) 1010 and a system connection 1005that couples various system components including the system memory 1015,such as read only memory (ROM) 1020 and random access memory (RAM) 1025,to the processor 1010. The system 1000 can include a cache of high-speedmemory connected directly with, in close proximity to, or integrated aspart of the processor 1010. The system 1000 can copy data from thememory 1015 and/or the storage device 1030 to the cache 1012 for quickaccess by the processor 1010. In this way, the cache can provide aperformance boost that avoids processor 1010 delays while waiting fordata. These and other modules can control or be configured to controlthe processor 1010 to perform various actions. Other system memory 1015may be available for use as well. The memory 1015 can include multipledifferent types of memory with different performance characteristics.The processor 1010 can include any general purpose processor and ahardware or software service, such as service 1 1032, service 2 1034,and service 3 1036 stored in storage device 1030, configured to controlthe processor 1010 as well as a special-purpose processor where softwareinstructions are incorporated into the actual processor design. Theprocessor 1010 may be a completely self-contained computing system,containing multiple cores or processors, a bus, memory controller,cache, etc. A multi-core processor may be symmetric or asymmetric.

To enable user interaction with the computing device 1000, an inputdevice 1045 can represent any number of input mechanisms, such as amicrophone for speech, a touch-sensitive screen for gesture or graphicalinput, keyboard, mouse, motion input, speech and so forth. An outputdevice 1035 can also be one or more of a number of output mechanismsknown to those of skill in the art. In some instances, multimodalsystems can enable a user to provide multiple types of input tocommunicate with the computing device 1000. The communications interface1040 can generally govern and manage the user input and system output.There is no restriction on operating on any particular hardwarearrangement and therefore the basic features here may easily besubstituted for improved hardware or firmware arrangements as they aredeveloped.

Storage device 1030 is a non-volatile memory and can be a hard disk orother types of computer readable media which can store data that areaccessible by a computer, such as magnetic cassettes, flash memorycards, solid state memory devices, digital versatile disks, cartridges,random access memories (RAMs) 1025, read only memory (ROM) 1020, andhybrids thereof.

The storage device 1030 can include services 1032, 1034, 1036 forcontrolling the processor 1010. Other hardware or software modules arecontemplated. The storage device 1030 can be connected to the systemconnection 1005. In one aspect, a hardware module that performs aparticular function can include the software component stored in acomputer-readable medium in connection with the necessary hardwarecomponents, such as the processor 1010, connection 1005, output device1035, and so forth, to carry out the function.

For clarity of explanation, in some instances the present technology maybe presented as including individual functional blocks includingfunctional blocks comprising devices, device components, steps orroutines in a method embodied in software, or combinations of hardwareand software.

In some embodiments the computer-readable storage devices, mediums, andmemories can include a cable or wireless signal containing a bit streamand the like. However, when mentioned, non-transitory computer-readablestorage media expressly exclude media such as energy, carrier signals,electromagnetic waves, and signals per se.

Methods according to the above-described examples can be implementedusing computer-executable instructions that are stored or otherwiseavailable from computer readable media. Such instructions can comprise,for example, instructions and data which cause or otherwise configure ageneral purpose computer, special purpose computer, or special purposeprocessing device to perform a certain function or group of functions.Portions of computer resources used can be accessible over a network.The computer executable instructions may be, for example, binaries,intermediate format instructions such as assembly language, firmware, orsource code. Examples of computer-readable media that may be used tostore instructions, information used, and/or information created duringmethods according to described examples include magnetic or opticaldisks, flash memory, USB devices provided with non-volatile memory,networked storage devices, and so on.

Devices implementing methods according to these disclosures can comprisehardware, firmware and/or software, and can take any of a variety ofform factors. Typical examples of such form factors include laptops,smart phones, small form factor personal computers, personal digitalassistants, rackmount devices, standalone devices, and so on.Functionality described herein also can be embodied in peripherals oradd-in cards. Such functionality can also be implemented on a circuitboard among different chips or different processes executing in a singledevice, by way of further example.

The instructions, media for conveying such instructions, computingresources for executing them, and other structures for supporting suchcomputing resources are means for providing the functions described inthese disclosures.

Although a variety of examples and other information was used to explainaspects within the scope of the appended claims, no limitation of theclaims should be implied based on particular features or arrangements insuch examples, as one of ordinary skill would be able to use theseexamples to derive a wide variety of implementations. Further andalthough some subject matter may have been described in languagespecific to examples of structural features and/or method steps, it isto be understood that the subject matter defined in the appended claimsis not necessarily limited to these described features or acts. Forexample, such functionality can be distributed differently or performedin components other than those identified herein. Rather, the describedfeatures and steps are disclosed as examples of components of systemsand methods within the scope of the appended claims.

Claim language reciting “at least one of” a set indicates that onemember of the set or multiple members of the set satisfy the claim. Forexample, claim language reciting “at least one of A and B” means A, B,or A and B.

What is claimed is:
 1. A method, comprising: receiving, by a protocolindependent multicast (PIM) backup designated router (BDR), from a PIMrouter located along a path between the PIM BDR and a source ofmulticast traffic associated with a multicast group, a first unicastmessage sent to a first address associated with the PIM BDR, the firstunicast message identifying a second address associated with the PIMrouter; storing, by the PIM BDR, the second address associated with thePIM router and a route used in delivering the first unicast message tothe PIM BDR; in response to a designated router migration triggeringevent, changing a first instance of a backup multicast tree state at thePIM BDR from blocking to forwarding, the backup multicast tree statebeing associated with the source of multicast traffic and the multicastgroup; and sending, by the PIM BDR to the PIM router through the routeused in delivering the first unicast message to the PIM BDR, a secondunicast message comprising an instruction to change a second instance ofthe backup multicast tree state at the PIM router from blocking toforwarding.
 2. The method of claim 1, wherein changing the firstinstance of the backup multicast tree state from blocking to forwardingand sending the second unicast message comprises changing a role of thePIM BDR from the BDR to an active PIM designated router (DR).
 3. Themethod of claim 2, further comprising sending, by the active PIM DR to anext hop towards the source of multicast traffic, one or more PIM joinmessages comprising active PIM joins based on the active PIM DRswitching to an active state from a backup state.
 4. The method of claim3, further comprising: receiving, by the next hop, the PIM join messagefrom the active PIM DR; and controlling a multicast tree state at thenext hop based on the PIM join message.
 5. The method of claim 4,further comprising: in response to receiving the PIM join message,determining that the next hop does not have the multicast tree stateassociated with the multicast group and the source of the multicasttraffic; and instantiating the multicast tree state at the next hop. 6.The method of claim 5, further comprising: storing, by the next hop, thefirst address associated with the active PIM DR as a unicast addressassociated with the active PIM DR; and sending, by the next hop, a copyof the PIM join message towards the PIM router, the copy of the PIM joinmessage identifying the first address associated with the active PIM DR.7. The method of claim 1, wherein the designated router migrationtriggering event includes a failure of a link between the PIM router anda PIM designated router (DR) associated with the multicast group and thesource of the multicast traffic.
 8. The method of claim 1, wherein thedesignated router migration triggering event includes a failure of a PIMdesignated router (DR) associated with the multicast group and thesource of the multicast traffic.
 9. The method of claim 1, wherein thedesignated router migration triggering event includes a failureassociated with one or more interfaces of one or more PIM routerslocated along an active path between a PIM designated router (DR)associated with the multicast group and the source of the multicasttraffic and the PIM router.
 10. A system comprising: one or moreprocessors; and a computer-readable medium comprising instructionsstored therein, which when executed by the one or more processors, causethe one or more processors to: receive, by a protocol independentmulticast (PIM) backup designated router (BDR), from a PIM routerlocated along a path between the PIM BDR and a source of multicasttraffic associated with a multicast group, a first unicast message sentto a first address associated with the PIM BDR, the first unicastmessage identifying a second address associated with the PIM router;store, by the PIM BDR, the second address associated with the PIM routerand a route used in delivering the first unicast message to the PIM BDR;change, in response to a designated router migration triggering event, afirst instance of a backup multicast tree state at the PIM BDR fromblocking to forwarding, the backup multicast tree state being associatedwith the source of multicast traffic and the multicast group; and send,by the PIM BDR to the PIM router through the route used in deliveringthe first unicast message to the PIM BDR, a second unicast messagecomprising an instruction to change a second instance of the backupmulticast tree state at the PIM router from blocking to forwarding. 11.The system of claim 10, wherein the instructions, which when executed bythe one or more processors, further cause the one or more processors tochange a role of the PIM BDR from the BDR to an active PIM designatedrouter (DR) as part of changing the first instance of the backupmulticast tree state from blocking to forwarding and sending the secondunicast message.
 12. The system of claim 11, wherein the instructions,which when executed by the one or more processors, further cause the oneor more processors to send, by the active PIM DR to a next hop towardsthe source of multicast traffic, one or more PIM join messagescomprising active PIM joins based on the active PIM DR switching to anactive state from a backup state.
 13. The system of claim 12, whereinthe instructions, which when executed by the one or more processors,further cause the one or more processors to: receive, by the next hop,the PIM join message from the active PIM DR; and control a multicasttree state at the next hop based on the PIM join message.
 14. The systemof claim 13, wherein the instructions, which when executed by the one ormore processors, further cause the one or more processors to: determine,in response to receiving the PIM join message, that the next hop doesnot have the multicast tree state associated with the multicast groupand the source of the multicast traffic; and instantiate the multicasttree state at the next hop.
 15. The system of claim 14, wherein theinstructions, which when executed by the one or more processors, furthercause the one or more processors to: store, by the next hop, the firstaddress associated with the active PIM DR as a unicast addressassociated with the active PIM DR; and send, by the next hop, a copy ofthe PIM join message towards the PIM router, the copy of the PIM joinmessage identifying the first address associated with the active PIM DR.16. The system of claim 11, wherein the designated router migrationtriggering event includes a failure of a link between the PIM router anda PIM designated router (DR) associated with the multicast group and thesource of the multicast traffic.
 17. The system of claim 11, wherein thedesignated router migration triggering event includes a failure of a PIMdesignated router (DR) associated with the multicast group and thesource of the multicast traffic.
 18. The system of claim 11, wherein thedesignated router migration triggering event includes a failureassociated with one or more interfaces of one or more PIM routerslocated along an active path between a PIM designated router (DR)associated with the multicast group and the source of the multicasttraffic and the PIM router.
 19. A non-transitory computer-readablestorage medium comprising instructions stored therein, which whenexecuted by one or more processors, cause the one or more processors to:receive, by a protocol independent multicast (PIM) backup designatedrouter (BDR), from a PIM router located along a path between the PIM BDRand a source of multicast traffic associated with a multicast group, afirst unicast message sent to a first address associated with the PIMBDR, the first unicast message identifying a second address associatedwith the PIM router; store, by the PIM BDR, the second addressassociated with the PIM router and a route used in delivering the firstunicast message to the PIM BDR; change, in response to a designatedrouter migration triggering event, a first instance of a backupmulticast tree state at the PIM BDR from blocking to forwarding, thebackup multicast tree state being associated with the source ofmulticast traffic and the multicast group; and send, by the PIM BDR tothe PIM router through the route used in delivering the first unicastmessage to the PIM BDR, a second unicast message comprising aninstruction to change a second instance of the backup multicast treestate at the PIM router from blocking to forwarding.
 20. Thenon-transitory computer-readable storage medium of claim 19, wherein theinstructions, which when executed by the one or more processors, furthercause the one or more processors to change a role of the PIM BDR fromthe BDR to an active PIM designated router (DR) as part of changing thefirst instance of the backup multicast tree state from blocking toforwarding and sending the second unicast message.